1. Field of the Invention
The present invention relates to a semiconductor device having a circuit which includes a thin film transistor (hereinafter called a TFT), and a manufacturing method thereof. For example, the present invention relates to an electronic appliance in which an electro-optic device typified by a liquid crystal display panel or a light-emitting display device having an organic light-emitting element is mounted as a part thereof.
In this specification, the semiconductor device includes general semiconductor devices that can function by using semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic appliance are all included in the semiconductor device.
2. Description of the Related Art
In recent years, attention has been focused on a technique for forming a thin film transistor (TFT) using a semiconductor thin film (with a thickness of about several nanometers to several hundred nanometers) formed over a substrate having an insulating surface. Thin film transistors are widely applied to electronic devices such as an IC and an electro-optical device. In particular, development is urgently required on thin film transistors as switching elements of image display devices.
In manufacturing of an electronic appliance having a semiconductor circuit, a mother glass substrate is used instead of a wafer substrate in order to improve efficiency for mass production, and a plurality of devices are often taken from one mother glass substrate. A mother glass substrate has a size of 300×400 mm for the first generation in the beginning of 1990, which has grown to 680×880 mm or 730×920 mm for the fourth generation in 2000. Production techniques have progressed so that a number of devices, typically display panels, can be taken from one substrate.
From now, in a film-forming method using a spin coating method, the increase in size of a substrate will be disadvantageous in mass production because a mechanism for rotating a large substrate becomes large, and loss and waste amount of a material liquid increase. Moreover, when a film is formed by spin-coating a rectangular substrate, circular unevenness with a rotating axis as a center is likely to appear on the film.
A droplet discharging technique typified by a piezo method or a thermal jet method, or a serial droplet discharging technique has attracted attention in recent years. This droplet discharging technique has been used in printing type and drawing an image on paper. Patent Document 1 discloses a technique for suppressing the displacement of a dot formation position and preventing deterioration of image quality by the use of a printing device having functions of a printer, a copier, a facsimile machine, and the like. Moreover, Patent Document 2 discloses a technique for recording an image in accordance with a head attachment angle θ at which the head is tilted to a straight line perpendicular to a direction where paper is to be delivered.
An attempt to apply a droplet discharging technique to a semiconductor field such as micropattern formation, which is completely different from a field of printing to paper or the like, has begun in recent years. For example, a method for forming a micropattern over a glass substrate by a droplet discharging technique is disclosed in Patent Document 3.
[Patent Document 1]
    Japanese Patent Laid-Open No. 2002-29097[Patent Document 2]    Japanese Patent Laid-Open No. 2001-30478[Patent Document 3]    Japanese Patent Laid-Open No. 2005-12179